1. Field of the Invention
The present invention relates to a technology for setting an optimum slew rate of a control signal regardless of compatibility with a host device.
2. Description of the Related Art
Conventionally, a slew rate of a control signal (an interface signal) exchanged between a host device and a storage device such as a magnetic disk device in a computer system is set on the basis of transfer mode supported by the storage device and the host device.
The slew rate is a rate of change in voltage of an output signal (time-dependent voltage change) when changing an output signal voltage according to a change in an input signal voltage, having a unit of volts per second [V/s].
The slew rate set in the storage device is set for each transfer mode separately on the basis of evaluation value at the time of shipment, or is set according to the transfer mode supported by the host device at the time of starting a computer as disclosed in Japanese Patent Application Laid-Open No. 2001-222474.
However, an electromagnetic interference (EMI) created within the computer system generates a noise in the interface signal. Such noise gives rise to multiple errors in the data read or the data write of the storage medium of the magnetic disk, which increases repetition of a retry and degrades a performance of the magnetic disk.
Thus, it is evident that changing a slew rate setting value of the interface signal is effective in preventing degradation of the performance caused by the EMI.
However, a degree of influence of the EMI differs according to compatibility of the host device with the storage device. Specifically, the degree of influence of the EMI differs according to an environment and a configuration of a computer system, even though the host device and the storage device connected together are of the same standard.
The degree of influence of the EMI cannot be estimated until the host device and the storage device are actually in operation after being connected together. Therefore, it is difficult to predict an optimum setting value for the slew rate to prevent degradation of the performance due to the EMI influence